diff --git a/mercurial/commands.py b/mercurial/commands.py
--- a/mercurial/commands.py
+++ b/mercurial/commands.py
@@ -1882,10 +1882,11 @@
         fm.startitem()
         fm.condwrite(ui.debugflag, 'source', '%s: ', source)
         if uniquesel:
-            fm.data(name=entryname, defaultvalue=defaultvalue)
+            fm.data(name=entryname)
             fm.write('value', '%s\n', value)
         else:
             fm.write('name value', '%s=%s\n', entryname, value)
+        fm.data(defaultvalue=defaultvalue)
         matched = True
     fm.end()
     if matched:
diff --git a/tests/test-config.t b/tests/test-config.t
--- a/tests/test-config.t
+++ b/tests/test-config.t
@@ -57,11 +57,13 @@
   $ hg showconfig Section -Tjson
   [
    {
+    "defaultvalue": null,
     "name": "Section.KeY",
     "source": "*.hgrc:*", (glob)
     "value": "Case Sensitive"
    },
    {
+    "defaultvalue": null,
     "name": "Section.key",
     "source": "*.hgrc:*", (glob)
     "value": "lower case"
@@ -77,8 +79,8 @@
    }
   ]
   $ hg showconfig -Tjson | tail -7
-   },
    {
+    "defaultvalue": null,
     "name": "*", (glob)
     "source": "*", (glob)
     "value": "*" (glob)